Wireless transceivers generate clocks, called Local Oscillators (LOs), used for down-conversion of received signals. The LOs are generated using a reference clock signal received from a Reference Oscillator circuit.
A frequency of the reference clock signal will from time to time vary from the desired frequency and therefore will need to be corrected. The frequency correction can be applied directly to the Reference Oscillator circuit or to a circuit that produces a replica of the reference clock signal. The amount of frequency correction needed may be determined using the received signals.
Any oscillator or clock circuit, whether uncorrected or corrected, will generate harmonic signals having respective frequencies that are integer multiples of the circuit's fundamental frequency. The harmonic signals may couple into sensitive receive circuits and interfere with the reception of the received signals.
A device may attempt to determine and cancel the interfering harmonic signals. In many wireless systems, such as cellular radio systems, the interference cancellation must be done very quickly, and as a result traditional feedback adaptive interference cancellation systems are not effective.